Homo- and copolymerization of vinyl monomers using tautomeric pyruvic acid derivative as catalysts



United States Patent 3,354,134 HOMO- AND COPOLYMERIZATION OF VINYL MONOMERS USING TAUTOMERIC PYRUVIC ACID DERIVATIVES AS CATALYSTS Heinrich Hopfi", Zurich, Switzerland, and Eduard Kleiner,

Ardsley, N.Y., assignors to Deutsche Goldand Silber- Scheideanstalt vormals Roessler, Frankfurt am Main, Germany No Drawing. Filed Nov. 10, 1964, Ser. No. 410,300 Claims priority, application Germany, Nov. 14, 1963, D 42,933 6 Claims. (Cl. 260-895) The present invention relates to an improved process for the homoor copolymerization of vinyl monomers.

It is known that vinyl monomers can be polymerized in bulk with radical forming catalysts. Such polymerized vinyl compounds are of great interest for the production of organic glasses. One disadvantage in the known polymerization processes resides in the fact that the bulk polymerization can only be caused to progress uniformly with great difiiculty and usually tends to an uncontrolled progress of the polymerization which greatly reduces the quality of the organic glasses obtained. In order that the polymerization could be controlled to some extent only very small quantities of radical forming catalysts were employed. The quantities were so small that the time required for the polymerization was very long, and for many technical applications too long.

An object of the invention is to provide for a polymerization of vinyl monomers which proceeds rapidly under daylight or exclusion of light but which is controllable during every moment thereof so that clear and streak free products are obtained.

According to the invention it was found that bubble and streak free products can be obtained if the homoor copolymerization of vinyl monomers is carried out in the presence of at least one tautomeric compound of the formulae:

R =H, alkyl of 1-3 carbon atoms, CN or aryl, preferably phenyl.

Esters and amides of acrylic or methacrylic acid and especially methyl methacrylate above all come into consideration as the vinyl monomers to be polymerized according to the invention. However, rapid and controllable polymerization of other vinyl monomers, such as, for example, acrylonitrile, vinyl carbazole, vinylpyrolidone, vinyl chloride, vinylidene chloride and styrene can also be effected with the catalysts according to the invention.

Suitable catalysts according to the invention, for in stance, are: phenyl pyruvic acid, its methyl or ethyl esters, its anilide, phenyl cyanopyruvic acid, diphenyl pyruvic acid. Phenyl pyruvic acid has proved particularly effective.

The quantities of the catalysts employed according to the invention can be varied within Wide limits and lie between 0.001 and 10% by weight with reference to the vinyl monomer to be polymerized. It is surprising that catalyst quantities of 10% by weight do not lead to an explosive course of polymerization as is the case with peroxide and azo compound catalysts.

In addition, the catalysts employed according to the invention can be used at practically any desired temperature, even higher temperatures. The polymerization temperatures do not depend upon the polymerization catalyst as is the case with peroxidic and azo catalysts, which decompose at higher temperatures, but are governed by the particular vinyl monomer concerned. The polymerization time therefore can be shortened by the use of elevated temperatures.

It was furthermore found that the polymerization initiating action of the catalysts according to the invention could be increased substantially by irradiation with UV light but that, on the other hand, room light or exclusion of light has little influence. Nevertheless, the catalysts according to the invention have the advantage over pure photosensitizers that even under the exclusion of light a polymerization accelerating effect is attained which leads to good polymerization yields. This effect is favored by a slight increase in temperature to, for example, -80 C.

The presence of oxygen has different influences on the catalytic effect achieved, depending upon whether the catalyst is present in keto or enol fonm. Whereas the catalyst effect of the keto form is increased by the exclusion of oxygen, traces of oxygen have to be present if the enol form is to have its maximum polymerization initiating action.

It is also of interest that the degree of purity of the vinyl monomers to be polymerized is of influence on the catalytic effectiveness of the catalysts according to the invention. It was found that the conversions with usual commercial, stabilized vinyl monomers with the catalysts according to the invention, whether in keto or in enol form, were higher than with freshly distilled monomers. It is possible therefore to polymerize commercial vinyl monomers directly with the catalysts according to the invention without the necessity of first subjecting them to a time consuming distillation.

Because of a certain sensitivity to oxidation the catalysts preferably are stored in admixture with plasticizers.

The catalysts according to the invention are preferably used in bulk polymerization but they also can be used in solution, precipitation, emulsion or suspension polymerizations.

The catalysts according to the invention are suited for homoand copolymerization of vinyl monomers and therefore the vinyl monomers can either be polymerized With themselves or copolymerized with other vinyl monomers. The polymerizations concerned herein therefore only involve vinyl monomers as the polymerizable component or components and do not concern, for example, copolyrnerization of vinyl monomers with unsaturated polyester resins. The term vinyl monomers is employed herein to signify monomers which undergo vinyl polymerization and contain a terminal CH =C group.

The catalysts employed according to the invention can also be used in combination with the usual catalysts, such as, peroxides or azo compounds. Naturally the latter can only be employed in very small quantities in order to avoid an explosive course of reaction.

Infra red spectra of polymethyl methacrylate which had been polymerized at C. in bulk with 0.5% by weight of phenyl pyruvic acid with reference to the starting monomer indicates that the polymethacryla-tes obtained were atactic. They are equal to those obtained Example 1 20 g. samples of methyl methacrylate which had been distilled in a silver plated high vacuum insulated distillation column 50 cm. high at about 50 C. under vacuum were each weighed into a reaction vessel with 0.5% of the catalysts given in the following Table 1. Subsequently the reaction vessel which was provided with a reflux condenser was rinsed minutes with 99.999% nitrogen and Example 2 The influence of UV light on the velocity of polymerization was investigated in the following manner:

10 g. samples of freshly distilled methyl methacrylate and the corresponding amount of catalyst were each weighed into a polymerization vessel. Thereupon the polymerization vessel was provided with a wide reflux condenser with a UV lamp and then rinsed with nitrogen for 5 minutes and dipped into a thermostatically controlled jacket provided With a sealing liquid. The catalysed samples were polymerized for one hour at 70 C. with constant stirring with a magnetic stirrer and constant passage of nitrogen. Some of the samples were polymerized while being irradiated with a 70 Watt high pressure mercury vapor lamp at a distance of 40 cm. and in comparison some of the samples were polymerized without such irradiation.

The results obtained are given in the following table:

TABLE 2 Percent Polymethyl- Polym. methacrylate Catalysts, 0.5% Formula time, nun.

With daylt. UV light Penyl pyruvic acid C tH5CHzC O C O OH 60 9. 9 11.8 Diacetyl CH -C OC O-C H3 60 3.8 14.4 Benzoin C 5H C HC O C (H5 45 2. G 17. 8

Control without cat- 60 0 1. 1

alyst.

then dipped into a thermostatically controlled jacket pro- Example 3 vided with a sealing liquid which maintained the polymerization temperature constant to 0.1" C. About every 15 minutes a small sample was pipetted out of the methyl methacrylate solution, which was maintained homogeneous by a magnetic stirrer, and such sample cooled to C. and the refractive index determined at 20 C. This method permitted conversions up to about 10 to 12% to be determined. With higher conversions homogeneous distribution could not be maintained in the polymerization vessel even with the aid of a magnetic stirrer. During the entire polymerization period a slight superatmospheric pressure was maintained in the system so that no air could enter. The results showed good reproducibility.

The refractive indices were exactly determined to four places with a Zeiss-Abbe-Refractometer Model A which was thermostatted to 20 C. by a Colora-U ltra thermostat type K. The calculation of the conversion to polymethyl methacrylate from the refractive index 11 was according to the formula employed by V. W. Smith (J. Amer. Chem. Soc., 68, 2059 (1946)), namely:

Percent polymethyl methacrylate: 1.22 X 10 X 11 wherein n =the difference between the refractive index of the monomer solution (inclusive of catalyst) and the refractive index of the monomer polymer solution after a certain poylmerization period.

*Catalyst having own yellow color.

In order to ascertain the influence of daylight and exclusion of light, 10 g. samples of methyl methacrylate were each polymerized at C. with 0.5% of the catalysts indicated in the following table in ampoules which had been sealed off with 99.999% nitrogen. The polymerization time was 1 hour. Exclusion of light was effected by enclosing the ampoules in aluminum foil.

In order to investigate the influence of oxygen, three different types of polymerization were carried out in ampoules. According to method A, the polymerization was carried out in open ampoules provided with reflux condensers, according to method B, the polymerization was carried out in ampoules which had been sealed under 99.999% nitrogen and according to method C, the polymerization was carried out in ampoules which had been rinsed with 99.999% nitrogen, subsequently frozen in a Dry Ice-acetone mixture and evacuated under high vacuum. In method C, after melting under nitrogen the procedure was repeated three times and finally the ampoules sealed under high vacuum and polymerized. In all instances the starting temperature for the polymerization was 0 C. After completion of the polymerization the ampoule content in each case was quenched in ice water and the conversion determined refractornetrically as in Example 1. The capacity of the ampoules was 20 cc. and the amount of methyl methacrylate introduced was 10 g.

The results are given in the following table:

TABLE 4 Percent Polymethyl- Polym. Polym. Methylmethacrylate Catalyst Percent time, Temp., methacrylate min. 0. Fresh d1stilled,g

A B C Phenyl pyruvic acid 100% 0.5 60 I 80 y 10 5. 7. 3 2.1

Example wherein R is selected from the group consisting of OH, Tests were carried out exactly as in Example 4 except OCH --OC H -OC H and NH-C H and R that technical stabilized methyl methacrylate was used is selected from the group consisting of hydrogen, CN

instead of freshly distilled methyl methacrylate. alkyl of 1-3 carbon atoms and aryl.

The results obtained are given in the following table: 2. The process of claim 1 in which the quantity of said TABLE 5 Percent Polymethyl- Polym Polym. Methylmethmethacrylate Catalyst Percent Time, Temp., acrylate Techn,

min. C. stabilized, g.

A B 1 C Phenyl pyruvic acid 0.5 60 80 10 10 11.2 i 2.1

Example 6 tautomeric compound employed is 0.001 to 10% by The polymerization initiating action of 1% of phenyl weight with reference to the monomer to be polymerized. pyruvic acid in the emulsion polymerization of methyl 3. The process of claim 1 in which phenyl pyruvic acid methacrylate is shown in the following table: is employed as the tautomeric compound.

TABLE 6.EMULSION POLYMERIZATION 0F METHYLMETHACRYLATE Polym. Polym. Conver- Monomer phase Aqueous phase Temp., Time, sion,

C. min. percent Methylmethacrylate, 10 g Water, 20 g r. 80 68. 7 Sodium Lauryl sulfate, 0.25 g Phenyl pyruvic acid,f0.1 g

The conversion indicated was determined gravimetri- 4O 4. The process of claim 1 in which the monomer is cally after precipitation from the emulsion with methanol a lower alkyl ester of methacrylic acid. and filter ng 01f the polymer. 5. The process of claim 1 in which the monomer is We clalm! methyl methacrylate. In a Process the Polymenzatlon of at least one 6. The process of claim 1 comprising in addition carryvinyl monomer cPntaining a terminal group, 45 ing out such polymerization under UV light initiated at a the step of carrying out such polymerizatlon 1n contact temperature between and with a catalytically effective amount of at least one tautomeric compound of the formulae: No references cited Gin-00430121 C=CCOR1 50 JOSEPH L. SCHOFER, Primary Examiner.

I W. WONG, Assistant Examiner. 

1. IN A PROCESS FOR THE POLYMERIZATION OF AT LEAST ONE VINYL MONOMER CONTAINING A TERMINAL CH2"C< GROUP, THE STEP OF CARRYING OUT SUCH POLYMERIZATION IN CONTACT WITH A CATALYTICALLY EFFECTIVE AMOUNT OF AT LEAST ONE TAUTOMERIC COMPOUND OF THE FORMULAE: 